Orthopedic surgical method, and structure for securing a bone screw to a bone

ABSTRACT

The present invention provides a method of forming pilot apertures for surgical screws. The method provides at least three points of contact to the screw shank to provide reliable positioning and retention of the bone screw. The method also provides slots or areas for insertion and retention of bone growth promoting materials which further secure the bone screw over time. The method is useful for patients of all ages, and may be particularly useful for patients that have osteoporosis or patients that are very active by providing additional securement of the bone screw to the underlying bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/743,620 filed on Jan. 15, 2020 (published as U.S. 2020-0222099),which is a nonprovisional application claiming priority to U.S.Provisional Patent Application No. 62/792,559, titled “ORTHOPEDICSURGICAL METHOD, SYSTEM AND STRUCTURE FOR SECURING A BONE SCREW TO ABONE”, filed Jan. 15, 2019 (expired). The contents of the abovereferenced applications are incorporated herein by reference in theirentireties for all purposes.

FIELD OF THE INVENTION

A surgical method of implanting an orthopedic screw and surgicalstructure.

BACKGROUND OF THE INVENTION

The present invention relates to a method, system and structure ofinstalling a surgical orthopedic screw to a patient's bone. Surgicalscrews, such as pedicle screws, are well known in the art, as are theirmethods of installation. One current method is to force form a pilothole with an instrument such as a Jamshidi needle; Jamshidi needles arewell known in the art. The screw is then installed by having itsthreaded shank threadably inserted into the formed hole by rotation ofthe screw shank. The pilot hole guides the screw movement on a desiredand predetermined path of movement. The pilot hole forming needle doesnot form machining residue. Such hole formation often requires a largeamount of force to effect its penetration. Such force can, however, behighly variable between patients and along the path of penetration, andthe bone structure changes from the bone exterior to interior. Inaddition, the screw shank diameter is typically much larger that thepilot hole diameter, often times requiring high torque being applied toeffect screw insertion.

A machining tool (or robotic effector) can form a machined pilot hole byremoving bone material. Such tools can include a drill bit thatprincipally cuts or machines with its tip end. Machining can alsoinclude cutting with the side of a cutting or grinding tool. Such toolsare rotated about their longitudinal axis or axis of rotation. Suchmachining creates machining residue that can interfere with screwinsertion. Generally, the diameter of the machined pilot hole is smallerthan the minor or root diameter of the screw so there is good strengthof screw attachment and threads are formed as the screw is inserted. Insome case, a thread forming tap is inserted prior to the screw to makescrew insertion easier and reduce the compressive load to the bonecaused by forcing the thread formation. The tap generally cuts thethreads by removing small amounts of material to form the threads.

It is often desirable to add material at orthopedic surgical sites toinduce bone growth around implants. Such materials include demineralizedbone, morselized bone, and bone cement to increase strength of thescrew/bone assembly. Current screw attachment methods preclude additionof such materials or cause the material to be wiped away as the screw isinserted. In the formation of pilot holes for screw insertion, there isno space between the screw shank and surface defining the pilot holeexcept at the tapered tip end of the screw. Thus, what is needed in theart is a screw aperture that provides three-point contact to the screwshank to provide positive positioning of the screw. The screw apertureshould also provide slots for addition of bone growth material tostrengthen the bond between the bone screw and the underlying bone.

DESCRIPTION OF THE PRIOR ART

The use and design of pedicle screws are disclosed in U.S. Pat. Nos.8,075,603 and 7,335,201. To the extent of a general description of thedetails and use of a pedicle screw, the disclosures of these patents areincorporated herein by reference.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a method of forming pilotapertures for surgical screws. The method provides at least three pointsof contact to the screw shank to provide reliable positioning andretention of the bone screw. The method also provides slots or areas forinsertion and retention of bone growth promoting materials which furthersecure the bone screw over time. The method is useful for patients ofall ages, and may be particularly useful for patients that haveosteoporosis or patients that are very active by providing additionalsecurement of the bone screw to the underlying bone.

Thus, it is an objective of the present invention to provide a methodfor installing orthopedic bone screws into bone.

It is another objective of the present invention to provide a method forinstalling orthopedic bone screws that is an improvement on currentprocesses and final surgical site structures.

It is a further objective of the present invention to provide a methodfor installing orthopedic bone screws that provides channels or slotsfor the use of bone growth material with a screw.

It is yet another objective of the present invention to provide anorthopedic surgical site for screw installation that can be used toinduce new bone growth.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with any accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention. Any drawings contained hereinconstitute a part of this specification, include exemplary embodimentsof the present invention, and illustrate various objects and featuresthereof.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an orthopedic skeletal surgical site showing a pilot hole forbone screw insertion;

FIG. 2 is a perspective view of the surgical site with a machiningeffector forming the pilot hole;

FIG. 3 is an isometric view of an example of a pedicle screw;

FIG. 4 is an isometric view of a skeletal bone with a pedicle screw inthe pilot hole of FIG. 1;

FIG. 5 is an isometric schematic view of the area of screw engagementwith a skeletal bone illustrating screw purchase with the bone;

FIG. 6 is an isometric view illustrating an alternative embodiment of apedicle screw having a tri-lobe shank at its minor diameter;

FIG. 7 is a section view taken along lines 7-7 of FIG. 6, illustratingthe cooperation of the shank with the bone;

FIG. 8 is an isometric section view taken along lines 8-8 of FIG. 6,illustrating the tri-lobe shank;

FIG. 9 is a partial section view taken along lines 9-9 of FIG. 6,illustrating the cooperation of the shank and thread with respect to thebone; and

FIG. 10 is an alternative construction of the pilot hole having fourlobes.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-10, a method, system and structure for securing abone screw to a bone in a surgical procedure is illustrated anddescribed. FIG. 3 illustrates a surgical screw in the form of a pediclescrew 11 useful with the present invention. As used herein, the screw11, when it has a cylindrical threaded shank section, has a major threaddiameter D that is the diameter of an imaginary coaxial cylinder thatjust touches the crest of an external thread in the cylindrical portionof the screw 11. It is to be understood that the shank 13 can be atapered shank. Such screws are self-tapping screws and preferably of agimlet style or cone point threaded shank 13. It is to be understood,however, that any suitable type of screw shank can be utilized for thescrew 11. While the present invention will be described in terms of theuse of a pedicle screw, it is to be understood that other types ofsurgical screws can be used. The screw shank 13, for a shank that has agenerally cylindrical shank section, has a minor or root diameter (asthat term is used in the art), which is the diameter of an imaginarycylinder that just touches the root 17 of the external thread 15 in itscylindrical portion of the screw 11. The root 17 is the bottom of thegroove between two flanking surfaces of the thread 15. The thread 15 canbe a single thread or a dual thread, as is known in the art. Thethreaded portion can have different pitch sections. A pedicle screw 11includes a tulip 19, as is known in the art, for securement of a rod(not shown) to the screw 11. The tulip 19 is pivotally mounted on theshank 13, as is well known in the art, for poly-axial pedicle screws. Itis to be understood that the pedicle screw 11 could be a monoaxial screwor the tulip could be fixed to the screw without departing from thescope of the invention. The screw shank 13 will be associated with adriver element (not shown), such as a spline, hex or other shapedsocket, which will provide a means for a driver to couple with the screw11 to drive it into an orthopedic feature, such as a vertebral bone 21.In the illustrated structure of FIG. 4, the bone 21 is a vertebra havinga pedicle portion 23. Preferably, the driver element is integral withthe shank 13. Such pedicle screws are well known in the art. The tulip19 can be internally threaded to receive a set screw (not shown) forsecuring a rod in the saddle portion 22 of the tulip 19. FIGS. 6-9illustrate an alternative embodiment of the screw 11. This embodiment ofthe screw 11 includes a tri-lobe shank 70 and standard threads forcooperation with a bone. In this embodiment, the shank 13 would providecompression to the innermost points of the pilot hole 33. Thisconstruction may be particularly useful for patients having osteoporosisby limiting the load to the surrounding bone while still compressing thebone sufficiently to gain a good purchase, and thus good pull outstrength to the screw 11. FIG. 7 illustrates the preferred crosssectional shape of the shank 13. FIG. 8 illustrates the relationship ofthe shank to the outer diameter of the threads 15. FIG. 9 illustratesthe areas of compression 72 provided by the cooperation of the shank 70and threads 15 to the shaped pilot hole 33.

FIGS. 1, 2 and 5 show a surgical site 31 with a pilot hole 33 useful forreceiving the shank 13 of a screw 11 therein. FIG. 2 shows the pilothole 33 with a hole forming effector 35 therein; while FIG. 5 shows thepilot hole 33 schematically with a shank 13 installed in the pilot hole33 and illustrates purchase areas 37. As used in the art, a purchasearea 37 is that area of engagement between a screw thread and bone whenthe screw shank 13 is in engagement with the bone in the cylindricalportion of the screw shank 13. As used herein, a purchase is that areaof engagement between the screw shank 13 and bone 21 in the area of theshank adjacent the tulip 19 or end portion of the screw 11 immediatelyadjacent the exposed outer surface of the bone 21 in which the screw 11is installed. The effector 35 is shown as having a machining element 41attached to a shaft 43, which in turn is coupled to a drive device (notshown) such as an electric motor or other powered rotary device. In apreferred embodiment, the shaft 43 would be coupled to a drive devicethat is part of a surgical robot (not shown) that will control operationof the machining element 41. A preferred machining element 41 would beable to machine bone with its distal or free end and on its side.Movement of the machining element 41 can be controlled in all three axesby the robot (not shown). Such robots are well known in the art. Such arobot is disclosed in our co-pending patent applications Ser. Nos.62/616,673; 62/681,462; 62/423,651; 62/616,700; 62/681,462 and Ser. No.15/816,861 to Peter L. Bono. Alternatively, the machining element 41 andthe remainder of the effector 35 can be coupled to a manually controlledpowered driver, such as an electric motor that is part of a surgicaltool as is known in the art. A manually operated powered driver witheffector 35 can be used in combination with a guide jig (not shown)suitably held in place to effect pilot hole formation.

The pilot hole 33 has a plurality of lobes 51, as best seen in FIG. 5.At least three lobes 51 are needed, while four lobes 51 are shown inFIG. 10. The lobes 51 project generally radially outwardly from a centerof the pilot hole 33, and preferably are spaced circumferentially atequal angles between one another. For example, if there are three lobes51, the angular spacing would be about 120° between the radial centerline of each of the lobes 51. In the case of four lobes, the spacingwould be about 90°. As seen in FIG. 1, the end 55 of each of the lobes51 is curved at least at the corners between the respective end 55 andthe walls 59 forming a channel 61. The lobes 51 overlap at a centralportion of the pilot hole 33 for receipt of the shank 13 therein.Spandrels 65 are formed in areas between adjacent walls 59 and provide atransition between adjacent lobes 51. The purchase areas 37 are formedin the spandrels 65.

After the pilot hole 33 is formed, as described above with the effector35, the screw 11 is threaded into the pilot hole with the thread 15 ofthe shank 13 engaging bone material in the purchase areas 37.Preferably, the entire depth of the thread 15, i.e., the surfacedefining the root 17 of the thread will be engaged with the bonematerial. Preferably, there will be interference between the rootsurface 14 and the bone 21. As best seen in FIG. 5, the angle A of theouter edge of the thread 15 engaging in the bone 21 will be in the rangeof between about 60° and about 200° of the outer perimeter of the thread15 at the outer surface of the bone 21 surrounding the shank 13. Theangle A measurement is taken at the top surface of the bone at the outerperimeter of the last full turn of the thread 15 engaging the bone 21.

In a preferred embodiment, each of the lobes 51 are sized and shaped toprovide an open space between the outer perimeter of the thread 15 andthe most radially outward portion of a respective end 55 of each of thelobes 51, a distance S of at least about ⅛ inch. This open area of thepilot hole 33 allows for the insertion of bone inducing growth material,such as demineralized bone, morselized bone, bone cement and the like,to be inserted into the pilot hole 33 to induce bone growth between thebone 21 and the portions of the screw thread 15 that are exposed in thepilot hole 33.

In the practice of the present invention, the surgical site 31 isexposed for the surgical procedure. The pilot hole 33 is formed with theeffector 35 by machining each of the lobes 51 to the desired position,size and shape, which will be determined by the screw to be used. Theshank 13 is then suitably driven into the pilot hole 33 with the thread15 engaging the purchase areas 37. The size and shape of the pilot hole33 will be determined by such factors as the major diameter of the shank13, the root diameter of the shank 13, and the quality of the bone 21,in addition to other factors as are known in the art. The selected screw11 is then driven into the pilot hole 33. If the screw 11 is a pediclescrew, then a rod or the like would be subsequently secured to the tulip19 as is known in the art.

The term “about”, as used herein regarding quantitative dimensions andangles, is used to recognize that those measurables cannot be measuredwith high precision using commonly available measuring devices, and thatthey are difficult to measure given the types of materials that arebeing measured; for example, rough and non-uniform. It is alsorecognized that different people measuring the same thing will oftenobtain different results, particularly given different measuringenvironments. These variations, though, are inconsequential to theinvention. The term also includes manufacturing limitations that resultin inexact cutting and measurements, particularly with respect tomaterials such as bone that vary from patient to patient.

All patents and publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains.

It is to be understood that while a certain form of the invention isillustrated, it is not to be limited to the specific form or arrangementherein described and shown. It will be apparent to those skilled in theart that various changes may be made without departing from the scope ofthe invention and that the invention is not to be considered limited towhat is shown and described in the specification and anydrawings/figures included herein.

One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objectives and obtain theends and advantages mentioned, as well as those inherent therein. Theembodiments, methods, procedures and techniques described herein arepresently representative of the preferred embodiments, are intended tobe exemplary, and are not intended as limitations on the scope. Changestherein and other uses will occur to those skilled in the art which areencompassed within the spirit of the invention and are defined by thescope of the appended claims. Although the invention has been describedin connection with specific preferred embodiments, it should beunderstood that the invention as claimed should not be unduly limited tosuch specific embodiments. Indeed, various modifications of thedescribed modes for carrying out the invention which are obvious tothose skilled in the art are intended to be within the scope of thefollowing claims.

What is claimed is:
 1. A method for securing a bone screw to a bone in asurgical procedure comprising: exposing a surgical site for the surgicalprocedure; providing a surgical screw, wherein the surgical screwincludes a cylindrical shank section, the shank portion having at leastone helical thread for engaging bone material, the at least one helicalthread having a major thread diameter that is the diameter of animaginary coaxial cylinder that just touches the crest of the at leastone helical thread, the surgical screw having a minor or root diameterwhich is the diameter of an imaginary cylinder that just touches theroot of said at least one helical thread; forming a pilot hole into abone of the surgical site, wherein the pilot hole includes a pluralityof lobes, each of the plurality of lobes projecting radially outwardlyfrom a center of the pilot hole, and spaced circumferentially apart withrespect to each other, each of the plurality of lobes overlapping at acentral portion of the pilot hole so that the pilot hole is sized forreceipt of the shank therein, spandrels formed in areas between adjacentwalls of the plurality of lobes provide a transition between adjacentlypositioned lobes, the spandrels forming purchase areas for the helicalthread, the plurality of lobes sized and shaped to provide an open spacebetween said major thread diameter and a most radially outward portionof a respective end of each said lobe; and driving the shank into thepilot hole.
 2. The method for securing a bone screw to a bone of claim 1wherein the open space between said major thread diameter and the mostradially outward portion of a respective end of each the lobe issufficient for the insertion of a bone inducing growth material.
 3. Themethod for securing a bone screw to a bone of claim 1 wherein the openspace between the major thread diameter and said most radially outwardportion of a respective end of each the lobe is sufficient for theinsertion of a plurality of bone fragments.
 4. The method for securing abone screw to a bone of claim 1 wherein the open space between the majorthread diameter and the most radially outward portion of a respectiveend of each of the plurality of lobes is at least one eighth of an inch.5. The method for securing a bone screw to a bone of claim 1 whereineach of the plurality of lobes are spaced at substantially equal angleswith respect to each other.
 6. The method for securing a bone screw to abone of claim 1 wherein the pilot hole includes at least three lobes. 7.The method for securing a bone screw to a bone of claim 1 wherein thepilot hole includes at least four lobes.
 8. The method for securing abone screw to a bone of claim 1 wherein the shank portion is tapered ata distal end thereof.
 9. The method for securing a bone screw to a boneof claim 8 wherein the surgical screw is self-tapping.
 10. The methodfor securing a bone screw to a bone of claim 1 wherein the shankincludes a plurality of lobes, an outer perimeter of each lobe includingsegments of the helical thread.
 11. The method for securing a bone screwto a bone of claim 10 wherein the shank includes three lobes.
 12. Themethod for securing a bone screw to a bone of claim 1 wherein thesurgical screw is a pedicle screw.
 13. The method for securing a bonescrew to a bone of claim 1 wherein the surgical screw is a poly-axialpedicle screw.
 14. The method for securing a bone screw to a bone ofclaim 1 wherein the surgical screw is a mono-axial pedicle screw. 15.The method for securing a bone screw to a bone of claim 1 including atleast one second helical thread positioned spaced apart and parallel tothe helical thread.
 16. The method for securing a bone screw to a boneof claim 1 wherein the helical thread includes two different threadpitches along the length of the helical thread.